Selective reduction



Aug. 1, 1933. A. E. GREENE SELECTIVE REDUCTION Filed July 16, 1931 E 1 TE .Q 47 1 \(x .m/N.\a KR K/ w M h fl T Patented Aug. 1, 1933 PATENTOFFICE SELECTIVE REDUCTION Albert E. Greene, Medina, Wash.

Application July 16, 1931, Serial No. 551,180, and

in Canada June 18, 1925 4 Claims.

.I have filed application in Canada, Serial No. 303,820, filed June18,1925.

My present invention relates to'metallurgical processes for thereduction of oxide ores, and par- 5 ticularly to an improved method ofselectively reducing one or more metal oxides contained in ore. Myprocess relates further to a process ofreduction at controlledrelatively low temperatures whereby iron is reduced from an iron orecontaining phosphorus without reduction of the phosphorus.

One object of my invention is to treat high phosphorus iron ore in orderto reduce the iron therefrom in a continuous manner while retain- 15,ing the phosphorus in the slag in chemical combination with certain slagforming oxides, namely calcium oxide and iron oxide. Another object ofmy invention is to control the reduction of iron oxide so as to onlypartly reduce it, whereby some of the oxide is retained in the slagwhere it serves to hold the phosphorus oxide in combination with calciumoxide so that the phosphorus is not reduced.

This application contains subject matter in common with my applicationsfor patent, Serial No. 726,541, filed July 17, 1924 (United StatesPatent No. 1,819,238) and Serial No. 34,041 filed June 1, 1925 (UnitedStates Patent No. 1,819,239).

The process of this invention consists in preparing a mixture of oxideore with calcium oxide or lime stone and also with carbonaceous reducingagent, such as coal, preferably all crushed relatively fine. Thisprepared mixture is fed into a smelting hearth furnace so that it moveson to a molten slag bath therein. The mixture may be preheated, or itmay even be partly reduced at temperatures below the sinteringtemperature before it is fed into the smelting hearth furnace. Thesmelting furnace is provided with heating 40 means such as electricheating means with or without fuel heating means. A bath of molten slagand reduced metal beneath is maintained. The prepared mixture, after itenters the smelting chamber, is heated to a temperature sufilcientlyhigh to cause reduction of the oxide of iron but not sufllciently highto fuse the reduced pure iron. Reduction results from the action of thecarbonaceous material. The mixture is preferably charged at one part orend of the smelting hearth where it can be heated to the reducingtemperature and then as reduction proceeds the mixture moves along onthe slag bath and the reduced iron passes down beneath the slag. At theother part of the bath heating may beincreasedsoaatoreadilyfusetheslagformingmaterials. The proportion ofcarbonaceous material is regulated in accordance with the temperatureand proportion of oxygen in the'atmosphere in the part of the smeltinghearth where the charge enters. It is regulated so as to not completelyreduce the oxide of iron inthe slag after the slag forming materialshave become fused. In this molten slag, it is desirable to maintain atleast 10% and preferably from 15% to 25% of oxide of iron and the slagwill also contain lime in-sufiicient amount to hold the phosphorus oxidecombined with the lime and iron oxide. The regulation of the proportionof carbonaceous material is governed by the extent to which combustiontakes place in the smelting hearth. A considerable excess of carbon maybe present in the charge entering the smelting hearth chamber and yetnot prevent the retaining of oxide of iron in the slag formed. That is,oxidation in the smelting chamber may dispose of this excess of carbonand by this means together with the control of temperature the ironoxide is not completely reduced and sufiicient is left to accomplish theholding of the phosphorus oxide from reduction.

I have carried out the process of this invention in two differentways,-in one, the iron oxide retained in the molten slag served to takeup practically all of'the carbon so that the reduced iron waspractically free of carbon. and in the other, the reduced iron containedcarbon but the temperature was such as to retain the phosphorus in theslag even in the presence of the carbonized iron. In the first mentionedkind of operation I have collected the reduced iron in very purecondition beneath the slag where it collected and remained in asemi-molten or solid condition. In the second kind of operation wherethe reduced iron contains a considerable amount of carbon, its meltingpoint is lowered and it remained molten beneath the slag.

My method may be carried out continuously by means of a continuous orregular feed of charge mixture and a tapping of slag at regularintervals. The reduced iron collects beneath the slag and can'be tappedafter it is raised in temperature sufiiciently. However, when pure ironcollects beneath the slag, the feed can be stopped and a reducing slagsubstituted for the oxide slag, and the metal can be finished under thisreducing slag without contamination.

Another feature of the process of my invention relates to sulphurremoval from the reduced metal, or rather to separation of sulphur whichmay be present in the charge. I have found that no under the conditionsof operation with a basic slag and the conditions described in theoperation of this process, sulphur is largely separated from the reducediron. I have found that coal may be used even though it contains aconsiderable amount of sulphur and yet the reduced iron can be madepractically free from sulphur. My proc-. ess is thus applicable for thetreatment of ore and use of carbonaceous material containing sulphur forthe production of low sulphur iron.

My invention may be carried out in different types of furnaces but Ihave found the kind of apparatus illustrated in the annexed drawingsatisfactory for the purpose.

In the annexed drawing,

Fig. 1 is an elevation partly in section, of apparatus which may beemployed for carrying out the process of the invention; and

Fig. 2 is a sectional elevation taken substan tially along line AA ofFig. 1.

The apparatus shown in the drawing comprises a smelting hearth chamber 1and a rotary preheating furnace 2 which communicates with a feed head 3.A plurality of charge pipes 4, 5, 6 and 7 extend between the feed head 3and openings in the chamber roof, indicated by the numerals 8 and 9, andprovide means for conduct ing charge material from the feed head to theinterior of the chamber. A stack 10 carries the flue gases away. Throughthis stack a screw conveyor 11 serves to carry the charge mixture intothe upper end of the rotary kiln 2. A ilue opening 12 is provided in theend of the smelting chamber for exit of gas. An opening is provided inthe feed head for a pipe 13 which may be extended to communicate withthe interior of the smelting chamberto provide means for conducting hotreducing gas from the smelting chamber into the feed head. Gas thusintroduced into the feed head may be mixed with air and burned in thelower end of the rotary kiln. The hearth of the smelting chamber slopestoward the tapping end. The tap hole 14 for metal is located adiacentthe lowermost end of the hearth. Metal and slag on the hearth of thesmelting chamber are indicated by the numerals 15 and 16, respectively.

A burnerl'l which may serve for admission of fuel and air when needed isprovided adjacent the tapping end of the smelting chamber. An opening 18through the roof serves for admission of. carbonaceous material andother material. An

electrode is shown at 19 and two others may be provided in the same lineacross the furnace for use of threephase current. A refractory wall,indicated in dotted lines at 20, having its bottom edge spaced above thehearth of the smelting chamber may be providedv adjacent the electrodesand'between the electrodes and the charging end of the smelting chamber.The provision of a wall such as that indicated by the numeral 20 results'in the establishment of separate chambers in which diiferenttemperatures may be established through the use of similar or differenttypes of heating means and/or in which different types of atmospheresmay be maintained.

A slag tapping spout 21 is provided. An air inlet 22 serves foradmission of air in controlled amounts for combustion in the chargingend portion of the furnace chamber.

Other types of furnaces such, frr example, as simple electric furnacesmay be employed in carrying out the process of the invention, but Iprefer to use 'an elongated furnace in order to provide for heating ofthe charge in a pile at the charging end at a relatively low temperatureand subsequent melting of the charge and completion of the operationunder the influence of electric heat at the tapping end. Where thecontinuous operation is carried on for a time and then the reduced metalfinished under a special slag, it is desirable to use a furnace whichmay be heated entirely by means of electric heat.

To illustrate the process of the inventiomthe treatment of an orecontaining approximately 83% of oxide of iron, 12% of silica, and .6%phosphorus and .'75% metallic manganese will be described. The ore iscrushed and preferably ground finely and mixed with ground or crushedcoal. In addition, limestone of about the same degree of fineness isprovided, although a coarser size limestone will serve. In place oflimestone, burnt lime could be used, but the excess heat of the processwill make it more economical to use limestone.

The proportions of these above mentioned constituents is determined bythe subsequent operations. The proportions are so regulated as to'maintain a slag containing preferably between. 15% and 25% percent ofcalcium oxide. The amount of coal or carbonaceous material in theoriginal charge may be varied somewhat, but an amount in excess of thatrequired for reducing the iron oxide of the ore should be provided, as aportion of the total amount will be consumed by the oxygen of air whichenters the furnace chamber. As long as the slag is maintained within thedesired limits so'that itwill hold the phosphorus from reduction, thenthe more carbon the better for preliminary reduction. The excess ofcarbon is main alned not greatly in excess of that actually used 1)reduce the oxide however.

The coal used may contain sulphur without this entering into the reducediron which collects T beneath the slag. This slag is preferably basic orat any rate contains a considerable proportion of lime, which mayaccount for the fact that n the iron can be reduced-free or practicallyfree 1 from sulphur.

The process is continuous in which case the prepared charge is fedregularly into the charging end of the smelting chamber and collects ina pile on the hearth where it gradually reduces 1 and then passes alongtoward the hotter end of the furnace where the arcs control thetempera-- ture.

The slag is melted by the time it reaches the slag end. Air can beadmitted through the inlet 1 pipes provided for the purpose so as tocarry on combustion towards the charging end. This can be done withoutserious loss of electrode material sincethe combustion takes placeawayfrom the electrodes. 1

Reductionof iron oxide takes place within the pile at the charging endof the furnace at relatively low temperatures. The temperature of thecharge here is well below the fusion temperature of pure iron. Thereduced iron collects in par- 1 ticlesor globules and passes downthrough the lz-yer of slag containing some iron oxide and thence intothe bath beneath the slag. The slag composition prevents reduction ofphosphorus If the process is carried out so as to collect very pure ironbeneath the slag, the iron may freeze. when sufficient iron hascollected, the feed of charge may be stopped and the slag replaced by alime-silica slag under which the pure metal may of oxide of iron and 55to 60 and also removes carbon from the reduced metal.

be superheated for pouring. In this way I have made iron ofapproximately 99.90% purity, which contained no single impurity in anamount 'exceeding .02%. That is the phosphorus, carbon, sulphur,silicon, and manganese were none .of them in excess of .02% each.

Iron can be reduced containing carbon but with the silicon held below 1%by means of a lime containing slag and a small amount of oxide of irontherein.

What I claim is:

1. The method of treating aniron ore containing phosphorus to reduce theiron and separate it from the phosphorus, said method comprisingpreparing a charge of crushed ore, carbonaceous material and calciumoxide material in proportions to not completely reduce the iron oxideand to form a slag containing at least ten percent of iron oxideand'over fifty'percent of calcium oxide, passing this charge into asmelting hearth chamher and heating it on a bath of molten slag thereinto a temperature sufficient to reduce the oxide of iron but insuflicientto reduce the phosphorus or fuse the charge, and subsequently fusing theslag forming materials and collecting the reduced iron beneath the slag.a

2. The method of reducing iron ore and separating the reduced iron fromphosphorus and sulphur contained in the charge materials, said methodconsisting in preparing a mixture of crushed ore, carbonaceous materialand calcium oxide material, charging this into a smelting chamber on amolten bath therein and heating it to a temperature sufliciently high toreduce iron oxide but not high enough to fuse the charge, maintaining anoxidizing slag on the bath and a basic flux therein ,in proportions tohold phosphorus and to prevent reduction of sulphur into the metal, andafter reducing the oxide of iron melting the remaining slag" materialelectrically, and collecting the reduced iron beneath the slag.

-3. The method of selectively reducing a metal from ore containing anoxide of the metal without reducing another element containedin the ore,the method consisting in preparing a charge of the ground ore,carbonaceous reducing agent and aflux for the oxide of the element to beretained unreduced, regulating the proportion of fluxingagent so as toform a basic slag with the oxide to be held in the slag, placing themixture on a molten bath in a smelting chamber and heating to atemperature sufliciently high to reduce the metal oxide but notsuflicient to melt the pure metal to be reduced, and subsequentlymelting the slag materials and collecting the reduced metal beneath.

4. The process of reducing oxide of iron and separating the iron fromphosphorus contained in the ore, said process consisting in preparing acharge of crushed ore, carbonaceous material and calcium oxide, passingthis into a reducing and smelting chamber in a pile above a molten bathof slag, controlling the proportion of carbonaceous material in theentering charge so as

